1. Field of the Invention
The present invention is directed to a voice sound input apparatus and a voice sound conference system.
2. Description of the Related Art
As voice conference systems capable of eliminating inconvenience and restrictions caused by cables, a voice conference system utilizing wireless communications is developed, as disclosed in JP-A-2002-344635.
Also, as voice input systems which may be applied to such voice conference systems, a close-talking type microphone apparatus utilizing a characteristic of a differential microphone is proposed, as disclosed in JP-A-2007-300513. Further, an arrangement in which an echo canceller is utilized as a noise canceller is proposed, as disclosed in JP-A-20041-120717.
In such a case that a unidirectional microphone is arranged by utilizing a plurality of microphones, under such an environment that surrounding noise is generated from one specific direction and only target sounds are generated from another specific direction, the target sounds can be acquired in a superior SNR (signal-to-noise ratio). However, as described in JP-A-2004-12071, if these plural sets of microphones are merely utilized as the unidirectional microphone in the above-described arrangement, then there is such a problem that when the surrounding noise is generated from another direction which is different from the above-explained specific direction, or noise is generated from the background located along the same direction as that of the target sounds, these noises cannot be canceled.
Also, in order to realize a high-precision noise eliminating function by utilizing a characteristic of a differential microphone, it is desirable to consider an adverse influence as to a delay distortion which is caused by a phase difference of sound waves which reach a plurality of microphones.